The present invention relates to thickness control method and system for a single-stand/multi-pass rolling mill.
In most of the conventional rolling mills, each stand has a single pass. Reduction ratio per stand is at most 40%. When a greater reduction is desired a tandem rolling mill comprising a plurality of stands is used.
However, a tandem rolling mill requires a large floor area for installation and is expensive.
As a measure to reduce the installation floor area, single-stand/multi-pass rolling mills are now drawing attention, in which three or more work rolls are arranged one above another between upper and lower back-up rolls to form a plurality of "passes". With the use of the single-stand/multi-pass rolling mill, the reduction ratio can be made as high as 70%. However, the single-stand/multi-pass rolling mill has a problem in that correction to the roll-gap position reference value for the purpose of controlling the final thickness affects not only the final thickness but also the thickness at the exit of other passes, e.g., the first pass, the second pass and the like. In other words, there is an interference between passes which forms an obstacle to improvement in accuracy of the thickness control. There has not been any satisfactory solution to this problem.